The invention relates to an electric machine with a slip ring and a brush holder.
An electric machine is a rotating machine which either as generator transforms mechanical energy into electric energy, or conversely, as an electric motor transforms electric energy into mechanical energy. The electric machine comprises a rotating rotor and a resting stator. The electric contact between rotor and stator is established through brushes. Such a brush is a component of the stator. As a springily guide slip contact it brings about the current transition to a moved machine part of the rotor, such as a collector or a slip ring. A brush is borne in a brush holder and is, as a rule, a press body of carbon, of natural-electro- or metal-graphite.
A brush is pressed, for example by a spring, onto a slip ring of the electric machine. By the movement of the slip ring the brush is slowly eroded. Hereby the press body becomes smaller by a few to several millimeters per operating hour. The material of the press body is ground into dust. The abrasion or brush dust is carried away from the brush by the air present in the electric machine, and it is distributed into the nearer and further environment of the brush. Here the brush dust settles as an electrically conductive layer on insulating parts of the electric machine and it can cause electric sparkovers there. The brush dust settles also on movable parts and bearings and causes there an increased frictional resistance.
The problem of the present invention is to give an electric machine which, even with a long-term use of several thousand hours, remains largely free from brush dust that deposits in undesired places.
This problem is solved by an electric machine with a slip ring and a brush holder, which according to the invention comprises a brush dust collecting device with a dust collecting head which is arranged in the immediate proximity of the slip ring.
The dust collecting head is formed in such manner that during the operation of the electric machine, brush dust arising on the brush holder is led into the dust collecting head. This is the case with a dust collecting head which is constructed as a vessel and that picks up dust dropping down from the brush holder. The dust collecting head can also be constructed in such manner that it collects dust that begins to be distributed from the brush holder into the environment. This happens as the dust collecting head is arranged where the dust from the brush holder is carried by air movement. The dust collecting head is constructed in such manner that it collects the dust or that the air carrying the dust can flow through the dust collecting head and the dust is conducted to a further component of the brush dust collecting arrangement.
The brush dust arises when the slip ring rubs on a brush of the electric machine. The slip ring transports the dust away from the brush holder. The dust, therefore, shortly after its arising is located directly on the slip ring. So that the dust can be collected before it can remove itself substantially from the slip ring into the electric machine, the dust collecting head is located in the immediate vicinity of the slip ring. xe2x80x9cimmediatexe2x80x9d means here that no other component of the electric machine is located between slip ring and dust collecting head.
By the invention it is achieved that a large part of the brush dust is collected into the dust collecting head directly after its arising, or if it is conducted through the dust collecting head, it collects into a further part of the brush dust collecting arrangement. The dust, therefore, no longer settles in undesired places of the electric machine. Short circuits caused by brush dust deposits or frictional losses in the movable parts of the electric machine are accordingly largely avoided. Since the electric machine, therefore, even with a long-time use of several thousand hours, remains substantially free from brush dust deposits in undesired places, the time intervals for necessary maintenance and cleaning operations can be increase. This leads to a good utilization of the machine and to low maintenance costs for the operator.
In a preferred development of the invention the dust collecting head comprises an inlet opening which, as viewed in rotating direction of the slip ring, is located immediately behind the brush holder. As described above, the slip ring transports the brush dust in rotation direction, away from the brushes. Behind the brush holder a part of the brush dust is released from the slip ring and is transported by the current of the air carried along by the slip ring in tangential direction to the slip ring. In a preferred form of execution of the invention, the inlet opening of the dust collecting head is located in tangential direction to the dust collecting head. In this manner the major part of the brush dust is caught up by the dust collecting head very rapidly after its arising; accordingly, it no longer passes to undesired places of the electric machine.
Expediently, a dust collecting head is allocated to each brush holder of the electric machine. Accordingly, the major part of the brush dust from all the brushes is collected. The allocation can be such that to each individual brush holder a single dust collecting head is allocated, therefore each dust collecting head collects the brush dust of the brushes from only one brush holder. It is also possible, however, so assign a brush collecting head to a group of brush holders, that collects the brush dust of all the brushes of the group.
A further advantage can be achieved by the means that the brush collecting head comprises a means that guides the brush dust from the inlet opening. Such a means can be, for example, a guide plate that guides the flow of air carried along from the slip ring into the dust collecting head. Such a means, however, can also be an opening of the dust collecting head, which opening is formed in such manner that the opening encloses one or more brush holders. This form of execution of the invention largely prevents the escape of the dust into zones of the electric machine in which the dust is undesired.
In a further advantageous development of the invention the dust collecting head and the brush holder, or the dust collecting head and a group of brush holders, form a compact component. Thus brush holders and brushes, for example, are tightly enclosed by the dust collecting head. The brush dust occurring is collected with utilization of the conveyance of the air from the slip ring. Alternatively, the brush holder or the brush holder group, for example, can be integrated into the dust collecting head. In such a dust collecting head that dust collecting head encompasses the brush holder or the brush holder group either completely or largely completely. In this form of execution of the invention the brush dust that leaves the brushes is essentially located in the dust collecting head already, and it can be transported off.
An integration of brush holder and dust collecting head in a compact component is also achieved if the dust collecting head is integrated into the brush holder or into a group of brush holders. This is the case, for example, when the dust collecting head essentially consists only of an opening in a brush holder, or of an interspace between brush holders, which is arranged so as to take up the arising dust, and which is provided with means that lead the brush dust into the opening. Hereby no separate dust collecting head is necessaryxe2x80x94which proves advantageous especially in the case of smaller electric machines, since in them there is frequently not enough room in the immediate vicinity of the brush holder for a separate dust collecting head.
In a further development of the invention the distance between the slip ring andxe2x80x94as seen in rotation direction of the slip ringxe2x80x94the front edge of the dust collecting head is greater that the distance between the slip ring and the rear edge of the dust collecting head In this manner the air carried along by the slip ring is pressed onto the front edge of the dust collecting head, into the free space between the slip ring and the dust collecting head Because of the slight distance between the slip ring and the rear edge of the dust collecting head the air, however, can poorly escape from the free space, so that between the slip ring and the dust collecting head a slight excess pressure is formed. By arranging the opening of the dust collecting head in the zone of this free space, the air carrying the brush dust with it is pressed into the dust collecting head by the rotary movement of the slip ring into the dust collecting head. The brush dust is thus transported into the dust collecting head.
Expediently the dust collecting head is made of a nonconducting material, for example a plastic material. With this form of execution of the invention the dust collecting head can be brought very close to the slip ring without there being present the risk of an electrical sparkover.
A farther advantage can be achieved by the means that the brush dust collecting device comprises a receiving container for the brush dust, and that the dust collecting head has an outlet opening which is connected with the collecting container by a pipe- or tube-system. In this manner the brush dust is led through the dust collecting head; it does not have to be stored in the dust collecting head. Furthermore, no device is needed inside the dust collecting head that serves for the separating of the brush dust from the air. The air carrying the brush dust is simply led through the dust collecting head into the collecting container in which the dust is separated and stored. The collecting container can lie inside or outside of the electric machine.
Expediently the brush collecting device comprises a suction fan The suction fan is intended to generate a subpressure in the dust collecting head. By the sub-pressure the dust-carrying air is drawn out of the environment of the brush holder into the dust collecting head. The dust collecting head thus functions as a brush dust suction nozzle, and like a dust suction nozzle, draws in the air present in the environment of the nozzle. The brush dust collecting device there is designed for example so that air can be drawn in through the entry opening of the dust collecting head and is conductable through the collecting container. In the collecting container the brush dust is separated from the air. Through this form of execution of the invention virtually all of the brush dust is transported from the brush holders into the brush dust collecting device, so that virtually no brush dust passes to undesired places of the electric machine.
Advantageously, the brush dust collecting device comprises a filter that is suited to retain brush dust in the collecting container.
The invention is especially well suited for an electric machine in which the rotor, and therewith also the slip ring, in operation, rotates about a vertical axis of rotation. Such a machine is used, for example, as generator in a hydrodynamic power plant In such a machine, as a rule because of the large number of brushes, a very large amount of brush dust arises. Furthermore, underneath the slip rings there are located further components of the electric machine and also further components of the hydrodynamic power plant which are especially sensitive to dust deposits. In such machines, therefore, it is especially advantageous to largely suppress the spreading of brush dust.